The present disclosure relates to a valve control apparatus for an internal combustion engine, and particularly relates to a valve control apparatus for controlling engine valve opening and closing operations in an internal combustor engine.
Internal combustion engines conventionally rely on poppet valves to regulate the supply of feed gas and expulsion of exhaust gas from cylinders of the engine. In particular, one or more intake valves regulate the supply of feed gas into a particular cylinder and one or more exhaust valves regulate the expulsion of exhaust gas from the same cylinder. Opening and closing of these valves are operated or controlled through rocker arms. More particularly, the intake and exhaust valves are normally maintained in a closed position by a biasing mechanism, such as conventional valve springs, and opened against the urging of the springs by a pivoting rocker arm imparting linear movement to the intake and exhaust valves.
In one arrangement, the rocker arms act as cam followers and transfer motion of a cam disposed on a rotating cam shaft to the valve. A cam can have a particular cam profile that is designed to open the valve such that the valve follows a desired opening and closing pattern. Traditionally, a single cam having a single cam profile operates one or more valves. An advancement over this traditional arrangement employs two or more rocker arms following two or more cam profiles for a particular valve or set of valves. In this advanced arrangement, the rocker arms for a particular valve or set of valves follow different cam profiles having particular optimized performance characteristics. For example, a cam associated with a particular rocker arm can have a profile designed to optimize engine performance when the engine is in a low RPM state or alternatively a high RPM state. The cam profile can also be designed to operate the engine in a high power mode or a high fuel efficiency mode. Multiple rocker arm systems, such as the foregoing, have been used to increase the power density (kW/L) of the engine, which can also allow for a smaller engine producing the same power. One such exemplary valve operating apparatus is described in commonly assigned U.S. Pat. No. 4,887,563, expressly incorporated herein by reference.
A variation on this technology allows for the valve motion (i.e., opening and closing) to be substantially deactivated, such as might be desirable when reducing the number of active cylinders during engine operation. Cylinder deactivation has been widely employed to temporarily decrease the number of operating cylinders in a multi-cylinder internal combustion engine to improve the engine's overall efficiency, particularly at light loads. This arrangement can include two rocker arms associated with a particular valve or set of valves. One of the rocker arms can connect to the particular valve or set of valves, while the other rocker arm can connect to a desired cam profile. A synchronizing pin having a longitudinal axis parallel to the rocker arms' rotating axis can connect and disconnect the rocker arms to and from one another. This allows the valve or set of valves to be actively following a cam profile or inactive, following no cam profile. Such synchronizing pins are pushed into and out of pairs of rocker arms by oil pressure supplied in changing paths. The synchronizing pins are limited to two positions, including a first position when oil pressure is low and a second position when oil pressure is high.
The number of rocker arms associated with a particular valve or set of valves, the number of rocker arms that can be connected together by synchronizing pins, and/or the number of synchronizing pins used in association with a particular valve or set of valves is sometimes limited. In particular, these can be limited due to size, weight and/or cost considerations. Competing considerations in engine design include downsizing the engine to improve fuel economy and increasing the amount of power generated by the engine. In addition, if three or more valve lift patterns are desired in an engine for one or more engine valves of a particular cylinder, several problems occur that potentially reduce performance of the engine. For example, to guarantee that the right valve lift pattern can be quickly chosen, all rocker arms must be connected during high engine RPM. The reciprocating mass of such a system of rocker arms becomes undesirably large.